The present invention relates to a measuring device suitable for measuring the density of a liquid such as a high-temperature melt. This measuring device is especially useful for receiving the density information of a semiconductive compound or metal melt which has substantial influences on crystal growth from the liquid phase.
A semiconductor device exhibits better performances as functions are integrated with higher density. The demand for the improvement of a semiconductor substrate in quality becomes stronger in response to the high-density integration. In order to develop the technical field of semiconductors, there are urgently required the settlement of the method which can control the inclusion of defects into a semiconductive crystal as well as the method which can manufacture a single crystal large in diameter for the enhancement of production efficiency.
The inclusion of defects in a semiconductive crystal is largely influenced by the liquid state of a melt. However, the liquid state of the melt is not yet made completely clear, since there is not an effective means for measuring the property of the high-temperature semiconductor melt with high accuracy in a short time.
The density of a high-temperature semiconductor melt is one of the factors which have large influences on the formation of defects in crystals.
Archimedes' method, i.e. a representative method for measuring the density of a liquid, uses the measuring device which has a bob 1 hung down with a suspensor wire 2, as shown in FIG. 1. The bob 1 is dipped in a liquid 3 whose density is to be measured. The weight of the bob 1 being dipped in the liquid 3 is measured by a balance 4. The density .rho. of the liquid 3 is calculated from the measured values according to the formula of: EQU .rho.=(M.sub.v -M.sub.1)/V.sub.b
wherein V.sub.b represents the volume of the measuring device to be dipped in the liquid 3, M.sub.v represents the weight of the measuring device measured by the balance 4 in a vacuum atmosphere, and M.sub.1 represents the weight of the measuring device dipped in the liquid 3.
The volume V.sub.b is previously detected by measuring the weight of the measuring device dipped in the liquid, e.g. water, whose precise density is already known. Hereby, the density .rho. of the liquid 3 is obtained from the difference between the weight My in vacuo and the weight M.sub.1 in the dipped state.
However, various errors originated in the properties of the liquid and the bob as well as a surface phenomenon are likely included in the measuring result obtained by Archimedes' method.
For instance, there is a surface tension between the suspensor wire 2 hanging the bob 1 and the liquid 3. Due to the surface tension, the surface of the liquid 3 in contact with the suspensor wire 2 is partially reformed into the state as shown in FIG. 2, so that the measuring device is affected by the upward force which makes the measuring result larger.
In case where the liquid 3 is heated at a high temperature by a heater provided around a crucible 6, a convection current is thermally formed in the liquid 3, as shown in FIG. 3. The descending flow at the central part applies a downward force to the bob 1, so that the measuring result is made smaller. In order to avoid the influence of the thermal convection 5, it is necessary to interrupt the heating of the liquid 3. As a result, it is difficult to measure the density of the liquid 3 at a constant temperature.
Besides, since the weight is measured under the condition that the bob 1 is dipped in the liquid 3, the bob 1 shall have apparent density larger than the density of the liquid 3. Otherwise, the bob 1 would float on the surface of the liquid 3, so that the density of the liquid 3 could not be measured. In addition, the bob 1 shall have a surface excellent in wettability to the liquid 3 and chemically stable against the attack of the liquid 3, and the bob 1 shall be made of a heat-resistant material which is not deformed by the heat of the liquid 3. Consequently, the bob 1 does not endure use for a long time, and there are various limitations on the material of the bob 1.